🔧 pottwal: Add alternative cert name for XMPP MUC

The config file /etc/dehydrated/domains.txt on the old host had this
line before:

        jabber.n39.eu conference.jabber.n39.eu

Link: https://github.com/24367dfa/ansible-role-dehydrated

pottwal.yml

@@ -35,6 +35,8 @@
           - name: sl.n39.eu
           - name: pad.n39.eu
           - name: "{{ prosody_domain_name }}"
+            alternate_names:
+              - conference.jabber.n39.eu
             deploy_cert_hook: "docker exec prosody prosodyctl --root cert import ${DOMAIN} /var/lib/dehydrated/certs"
     - role: penguineer.dehydrated_cron
     - role: dd24-dyndns-cron